1. Technical Field of the Invention
The present invention relates generally to an apparatus for igniting fuel for an internal combustion engine. More particularly, the present invention relates to an improvement of an apparatus for igniting fuel for an internal combustion engine wherein a controlling section for an igniter including a hybrid IC is firmly secured to a housing for a distributor, one of the signal lead wires extending from a signal pickup is earthed and moreover an earthing pattern on the hybrid IC is earthed via the distributor housing.
2. Description of the Background Art
A conventional apparatus for igniting fuel for an internal combustion engine including a hybrid IC is constructed such that one of the lead wires extending from a signal pickup located opposite to a rotor of a signal generator is earthed and moreover an earthing pattern on the hybrid IC is also earthed via a housing for a distributor. However, the conventional apparatus as constructed in the above-described manner is problematic in that an earthing circuit is constituted of many components and fabrication of the apparatus necessitates the expenditure of many manhours and provides low reliability at a high cost.
In a case where the earthing pattern on the hybrid IC is electrically connected to a heat sink by wire bonding or via a lead wire, the kind of material required for the heat sink is limited only to a specific material. Additionally, it is required that the heat sink is subjected to particular surface treatment, e.g., plating.
The conventional apparatus will be described further below with reference to FIGS. 4 to 6.
FIG. 4 is a wiring diagram which illustrates a controlling section of an igniter for the conventional apparatus.
In response to an ignition timing signal outputted from a signal generator, the controlling section is activated such that the signal is transmitted to an ignition coil 25 via a wave form correcting circuit 22, a drive circuit 23 and a power transistor 24. As is apparent from the drawing, one of the lead wires 21 extending from the signal generator 20 is earthed. The apparatus includes a power supply source 26 which is electrically connected to the respective components.
Referring to FIGS. 5 and 6 which illustrate the conventional apparatus, a frame 5 for the igniter controlling section 3 molded of non-electrically conductive synthetic resin is firmly secured to an electrically conductive housing 1 for a distributor by a plurality of tightening screws 4 via a heat sink 2 placed on the distributor housing 1 which is earthed. A hybird IC 6 is arranged in the frame 5 in contact with the heat sink 2. The frame 5 is closed by a cover 7.
Signal lead wires such as 21 extending from a signal pickup 14 located opposite to a rotor 13 for the signal generator 20 are fixed to the non-electrically conductive frame 5 by a plurality of tightening screws 16 in cooperation with the corresponding nuts 17 along with washers 15 and a terminal plate 11. As shown in FIG. 6, the signal lead wire 21 is electrically connected to the housing 1 via the terminal plate 11, a lead wire 10 soldered to an earthing pattern 8 on the hybrid IC 6, a connecting piece 9 and the heat sink 2.
As far as the conventional apparatus as shown in FIGS. 4 to 6 is concerned, an earthing circuit for the lead wires 21 is constructed such that electrical connection is made in accordance with the following steps: connecting the signal lead wire 21--tightening of the terminal plate 11 by the tightening screws 16--welding or soldering of the terminal plate 11 to the lead wire 10--soldering of the lead wire 10 to the earthing pattern 8 on the hybrid IC 6--bonding of the earthing pattern 8 to the heat sink 2--contacting of the heat sink 2 with the frame 5 by the tightening screws 4.
With such a construction, there arise problems that the apparatus is unavoidably constituted of many components with a large number of manhours being expended with only a low level of reliability being obtained a high cost.
As is best seen in FIG. 6, the earthing pattern 8 on the hybrid IC 6 is connected to the heat sink 2 via a wire bonding represented by reference numeral 9. Alternatively, soldering may be substituted for the wire bonding 9. In this case, the earthing pattern 8 on the hybrid IC 6 is connected to the heat sink 2 via the soldering so that the heat sink 2 is earthed via the housing 1 which is held in contact with the heat sink 2. With the conventional apparatus as constructed in that way, since the earthing pattern 8 on the hybrid IC 6 is electrically connected to the housing 1 via the wire bonding or soldering 9 and the heat sink 2, the kind of material required for the heat sink 2 is limited only to a specific material due to necessity for the wire bonding or soldering for the lead wire. Otherwise, it is required that the heat sink 2 is subjected to particular surface treatment, e.g., plating.